This invention relates to the nephelometric immunoassay which is one of immunoassays for measuring various components contained in body fluids such as blood and urine, for example, various sorts of immunoglobulins etc., and also to a nephelometer therefor.
In the nephelometric immunoassay wherein an antigen-antibody complex formed by an antigen-antibody reaction is measured by a light scattering photometer, there is a relationship as schematically shown in FIG. 1 between the light scattering intensity and the antigen concentration, and hence, two different values of antigen concentrations are obtained for one light scattering intensity. Therefore, even when the measurement is performed in a range 1 in FIG. 1 by adjusting the dilution ratio of a sample, etc., the measured sample sometimes contains an unexpectedly high concentration of antigen, and the measurement is feared to actually proceed in a range of antigen excess 2 in FIG. 1. In a prior-art method, accordingly, two specimens of unequal dilution ratios are prepared and measured for each sample. It is decided by studying the proportional relation between the light scattering intensity and the dilution ratio that the specimen falls in the range 1 in FIG. 1, and the value of a correct antigen concentration is obtained. Therefore, much labor and many specimens are required for the measurement.